Nutrition of Threonine

Part IV. Changes in Activities of Threonine Decomposition Enzymes in Rat Liver by Exeess Feeding of Lysine and Threonine

Abstract

The threonine content in blood and urine increased and threonine decomposition ability in liver decreased by feeding lower level of lysine, whereas threonine content in blood and urine decreased and the ability of liver increased gradually with increasing lysine content in diet. These phenomena were owing to the increase of threonine dehydratase activity of liver, which was measured from produced α-ketobutyric acid amount, by excess administration of lysine. The phenomena that threonine content in urine decreased and threonine decomposition ability of liver increased with increasing threonine content in diet when adequate amount of lysine was fed, were also ascribed to the increase of the dehydratase activity.
One m mole of threonine was incubated with liver homogenate in presence of PALP^*** at pH 8.2 for 20 and 30min and α-ketobutyric acid produced was introduced to its 2, 4-dinitrophenylhydrazone, which was chromatographed on silica-gel thin-layer plate and determined spectrophotometrically at 395mμ under N, N-dimethylformamide.
Other enzyme systems relating to threonine catabolism were also investigated, including threonine aldolase, threonine dehydrogenase and ornithine transaminase, showing no significant changes in activities by excess administration of lysine and/or threonine.